1. Field of the Invention
This invention relates to a DC regulated power source apparatus, and more particularly to a DC regulated power source incorporated in an electronic device.
2. Description of the Prior
Electronic devices, such as communications equipment or sequence controllers and numerical control units for controlling machine tools, generally incorporate a DC regulated power source device which supplies their electronic components with a regulated DC voltage. These DC regulated power sources include a reference power source for generating a reference voltage, as well as an output voltage control element. The output voltage control element such as a differential amplifier constantly compares the output voltage against the reference voltage and functions to hold the output voltage constant at all times by restoring the output voltage to the reference voltage when the former attempts to rise, or by raising the output voltage up to the reference voltage when the former attempts to drop.
The DC regulated power source devices referred to above usually produce the reference voltage through use of a Zener diode. However, since Zener voltages can differ slightly even for Zener diodes of the same type or grade, using the voltage obtained from such diodes as a reference voltage results in irregularities among the devices that receive the output voltage from the DC regulated apparatus. It is therefore conventional practice to employ a Zener diode of a higher Zener voltage than the reference voltage, and to divide this high Zener voltage down to an accurate reference voltage by means of a potentiometer.
When a machine tool is inspected or subjected to maintenance after installation in a factory, or when an inspection is carried out during the course of manufacture, there are cases where an operating margin test is conducted by shifting the operating voltage of a numerical control unit or sequence controller in the plus or minus direction by a prescribed value with respect to a rated voltage. When varying the voltage in this fashion, it is conventional practice to rotate, by small increments, the potentiometer which is used to divide the Zener voltage, thereby shifting the output voltage toward a prescribed value while closely observing an output voltmeter.
On the other hand, a hardware operating check has been facilitated greatly by automating the checking procedure or by providing machine tools, or the electronic devices which they incorporate, with a self-diagnosing function. It would be very convenient if the operating margin check could be included with the other operating checks since this would permit a confirmation of the operating margin of the circuitry. However, since the output voltage has been required to be adjusted by the manual operation of a potentiometer as described above, it has not been possible to insert into a series of automated testing steps an additional test step for confirming the operating margin of the circuitry.